This invention pertains to collagen compositions and methods of preparing such compositions.
Collagen is usually found as the principal protein component of the extra-cellular matrix. In mammals, collagen sometimes constitutes as much as 60% of the total body protein. It comprises most of the organic matter of skin, tendons, bones and teeth, and occurs as fibrous inclusions in most other body structures. Collagen is a relatively weak immunogen, due in part to masking of potential antigenic determinants by the helical structure. This helical structure also makes collagen resistant to proteolysis. Collagen is a natural substance for cell adhesion and the major tensile load-bearing component of the musculo-skeletal system. Because of the foregoing properties, collagen has application in the manufacture of implantable prostheses, and in the preparation of living tissue equivalents.
Collagen is an essential component of living tissue equivalents which are prepared from a hydrated collagen lattice contracted by a contractile agent, such as fibroblast cells, smooth muscle cells or blood platelets. Such tissue equivalents are disclosed in U.S. Pat. Nos. 4,485,096; 4,485,097; 4,539,716, 4,546,500; 4,604,346; 4,835,102; and 4,837,379, all of which are incorporated herein by reference (hereinafter collectively referred to as "the Patents"). These tissue equivalents include, but are not limited to, equivalents of epithelial tissue and connective tissue such as skin, cartilage, bone, blood vessels, and comprise living cells and extracellular matrix molecules, principally collagen, and may optionally be provided with components not typically found in normal tissue. Such tissue equivalents have a broad range of applications including applications in research and development, tissue and organ replacement and testing.
Collagen compositions are typically prepared from skin and tendons by procedures involving acid or enzyme extraction. Enzyme extraction is preferable in many instances because this methodology produces increased yields and higher purity collagen. However, enzyme extraction suffers the disadvantage of producing partically degraded collagen, i.e., the extraction enzymes cleave the collagen molecule at the terminal non-helical regions which contain the inter-collagenous cross-linkages.
It has been found that collagen extracted by use of the enzyme pepsin, a frequently used enzyme for the production of enzyme extracted collagen, produces living tissue equivalents which are undesirably weak for certain applications, e.g., those which involve substantial mechanical handling of the tissue equivalent. Thus, improved collagen compositions and methods of preparing such compositions are being sought.